1. Field of the Invention
This invention relates generally to breakaway pipeline couplings designed to separate when subjected to externally applied tensile loads exceeding a predetermined limit in order to prevent structural damage to other piping components. More particularly, this invention relates to breakaway pipeline couplings utilizing pressure compensating mechanisms to counteract tensile loads produced by internal pressure which might otherwise cause the coupling to separate.
2. Description of the Prior Art
Breakaway pipeline couplings for use in pipelines for transmitting oil, gas and other fluids are known. One commercially available breakaway pipe coupling is described in U.S. Pat. No. 4,059,288, issued Nov. 22, 1977 to Harvey O. Mohr. Another commercially available breakaway pipe coupling is described in European Patent application Publication No. 0006278A1, by Gall Thomson, published Jan. 9, 1980.
The Mohr patent discloses a separable safety pipeline connector which will separate at a predetermined externally applied tension, but which will be insensitive to variations in tension caused by internal pipeline pressure. The connector includes a housing having one axial end adapted for connection to the pipeline, and with the other axial end open. The connector includes a pipe extension member having one axial end adapted for connection to the pipeline for transmission of line fluids therethrough and with the other axial end arranged to telescope coaxially with the housing in sealed relationship therewith. A shear disc is mounted beween the housing and extension member for restraining the same against axial separation in response to axial tension loads applied thereto. The shear disc is sized to rupture at a predetermined axial load level, so that axial separation is prevented below such a load level. The housing and extension member define an annular chamber therebetween, whereby fluid pressure within the chamber forces the housing and extension member axially together to thereby balance line pressure. A port is provided through the extension member to communicate line pressure to the chamber.
The pressure balanced, breakaway pipe couplings disclosed by both the aforementioned Mohr patent and Thompson application recognize the need for compensating internal pipeline pressures, but do not address other structural and functional needs. For example, both the aforementioned couplings are expensive to fabricate and install, due, at least in part, to the several large-diameter, concentric, precision machined surfaces which must be provided in the pressure compensation chamber and piston apparatus. Furthermore, the Mohr coupling makes no provision for terminating the fluid flow through the coupling upon its separation, thus allowing the contents of the pipeline to be discharged into the environment.